Device for the continuous filteration of molten plastic material

ABSTRACT

A continuous filtration device for molten plastic materials that employs a filtration mesh that enters and exits the filtration chamber, resting against the outer surface of a perforated hollow cylinder, without losing any molten material during the replacement of the mesh and without tearing even when operating at high pressures inside the filtration chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Italian Patent Application 102020000020824, filed on Sep. 1, 2020, and is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

Not Applicable.

FIELD OF THE INVENTION

This invention relates to a device for the continuous filtering of molten plastic that uses a mesh filter belt.

BACKGROUND

A system for filtering plastic material is known, from the same applicant, namely patent EP1550544 which is referred to and incorporated by reference.

Said known filtering system is comprised of a device for the automated continuous cleaning of contaminated plastic material in the molten state by means of a metal mesh belt with a suitable weft.

The known device for the continuous filtering of molten plastic consists of a chamber inside a body with an opening for the entry of the plastic material to be filtered and an opening for the exit of the filtered plastic material; there is also an opening for the continuous entry and exit of a quite narrow metal mesh that, when crossed by said molten plastic materials, filters their contaminants; said metal mesh strip inside said chamber is resting against the outer surface of a hollow perforated cylinder that rotates around its main axis, a pair of sealing rollers, parallel to the hollow perforated cylinder, delimit the portion of the mesh strip resting against said perforated hollow cylinder, where said pair of sealing rollers with a metal mesh interposed between them and the perforated hollow cylinder, generates the sealing of the molten plastic material entering from the inlet opening, and also a further pair of rollers accompanying the mesh, parallel to the sealing rollers, to which an inlet and an outlet branch of the metal mesh are attached respectively, and a further floating roller placed with the inlet and outlet mesh branches interposed resting above the accompanying rollers centrally in the their interspace.

Said known device is able to successfully achieve its purpose for averagely polluted material and with high pressures that are not excessively high.

However, said known system appears to exhibit unsatisfactory behaviour when there are critical conditions, namely when there are materials that are highly polluted and/or there are high pressures, since in said system there could sometimes be a tear in the mesh and/or a small, albeit appreciable, loss of material through the inlet/outlet opening.

Since the demand for filtering is become much more intensive, both for materials with different characteristics and with different levels of contamination, which is increasingly rising to values that could not be treated in the past, the known filtering system is no longer adequate.

SUMMARY OF THE INVENTION Objects of the Invention

The object of the present invention is to make available a filtering device that can overcome one or more of the drawbacks set out above.

An important object of the present invention is to make available a filtering device that can easily remove contaminants from plastic material.

An important object of the present invention is to make available a filtering device that can also operate at high pressures.

An essential object of the present invention is to make available a filtering device that, within the scope of the preceding object, carries out the filtration with sufficient continuity, without the metal mesh suddenly breaking.

An equally important object of the present invention is to make available a filtering device that, within the scope of one or more of the preceding objects, allows at least a partial change of the mesh without interrupting the work flow.

Another object of the present invention is to make available a filtering device that limits and reduces, with respect to known devices, the loss of molten plastic, especially when the metal mesh has to be changed.

All the aforesaid objects, and others which will become more apparent from the continuation of the description, are obtained from the invention characterised by the features highlighted in the claims.

Explanation of the Invention

All the aforesaid objects are achieved and solved by the filtering device according to the claims.

In particular, the filtering device comprises

a body,

a chamber inside said body,

a hollow perforated cylinder that rotates around its main axis inside said chamber,

an inlet opening on the body for the entry into the chamber of the plastic material to be filtered, and

an outlet opening for the exit of the filtered plastic material from the body,

a connecting opening that connects the outside of the body with said internal chamber,

a filtration mesh strip that enters the chamber through said connection opening and exits through said connection opening after having carried out the filtration; where

-   -   a section of inlet-mesh that enters the chamber from the outside         of the body through an inlet path, and continuously moving         forward,     -   a stretch of the adjoining-mesh that remains attached to the         outer surface of said hollow perforated cylinder, and         continuously moving forward,     -   a section of outlet-mesh that exits the body from the chamber         through an exit path,

where said inlet-mesh, said resting-mesh and said outlet-mesh, a continuous belt, and a movable cone that creates, together with the body, said entry path and said exit path, where said cone can move between a first closing position and a second opening position on the opening that connects the exterior of the body with said chamber and that, in the first closing position, closes the entry path and closes the exit path and in the second opening position opens the entry path and opens the exit path;

where said entry path is a first channel between the outside of the body and the inside of the chamber, with a width corresponding to the width of the mesh belt and enclosed between the body itself and a first side wall of the cone

and where said exit path is a second channel between the outside of the body and the inside of the chamber, with a width corresponding to the width of the mesh strip and enclosed between the body itself and a second side wall of the cone

and where said cone has a base wall between said first and said second side wall, facing towards the inside of the chamber, facing the perforated hollow cylinder.

Said mobile cone in the closed position is close to the walls of the connection opening, with the inlet-mesh strip interposed in the inlet path and the outlet-mesh strip interposed in the exit path, preventing the melted plastic material within the chamber inside the body from escaping.

Said movable cone in the open position is spaced apart from the connecting opening walls, since said inlet-mesh can slide in the inlet path to enter the chamber inside the body, and said mesh-outlet can slide in the outlet path to exit the chamber inside the body.

Advantageous Characteristics of the Invention

Advantageously, said base wall of said cone has a profile corresponding to the underlying circular arc of the perforated hollow cylinder, limiting the molten material between the outer wall of the hollow cylinder and the base wall of said cone.

Advantageously, said cone is moved by an actuator externally joined to the cusp of said cone, resulting in a linear movement symmetrically established with respect to the cone.

Advantageously, said cone and/or said body at the inlet and/or outlet paths of the filtering mesh have plates of hardened/bonded material, limiting the wear of the corresponding walls during the relative movement of said mesh.

Advantageously, said body has an opening between the inside of the hollow and an accumulation tank for accumulating the molten material during the change and replacement of the mesh clogged by the contamination of the molten material, reducing the pressure inside the chamber.

Advantageously, said accumulation tank is a variable volume tank and has a movable piston that defines the capacity of the tank, and whose movement to increase the capacity favours the accumulation of the molten material coming from the cavity of the chamber and whose movement to decrease the capacity favours the return of the molten material into the cavity of the chamber.

Advantageously, said body has a valved opening between the inside of the cavity and the outside of the body in order to be able to open, by acting on said valve inserted in said opening, releasing the molten material coming from the hollow chamber of the chamber and reducing the pressure inside the chamber.

Advantageously, the aforesaid opening towards the accumulation tank and the aforesaid valved opening, by decreasing the pressure inside the chamber when the clogged mesh is changed and replaced, allow the size of the actuator that moves the said cone to be limited.

Advantageously, said device is provided on the outside of the body with a winder/advancing device for storing/advancing the clogged filtration mesh exiting the body.

Advantageously, said winder/feeder is motorised with a feed that keeps said clogged filtration mesh under tension when exiting the body.

Advantageously, the motorisation of said winder is provided with a torque control and a clutch that prevent the clogged filtration mesh from being torn.

DESCRIPTION OF THE DRAWINGS

The technical characteristics of the invention, according to the aforementioned objects, can be clearly seen from the content of the claims below and the relative results will be apparent in the detailed description that follows with reference to the drawings, which illustrate a purely exemplary and non-limiting embodiment, in which:

FIGS. 1-3 show the filtering device of the invention according to two perspective views and a front plan view;

FIGS. 4-6 show what is shown in FIGS. 1 to 3 without the front cover, showing the chFamber inside the body with the inner hollow perforated cylinder;

FIGS. 7-9 show what is shown in FIGS. 4 to 6 in an enlarged manner with greater detail;

FIG. 10 shows the filtering device in section according to a vertical plane passing through the main axis of the perforated hollow cylinder;

FIG. 11 shows what is shown in FIG. 10 in an enlarged manner with greater detail;

FIG. 12 shows the filtering device according to a perspective view and in a section composed according to a vertical plane and a horizontal plane passing through the main axis of the cylinder; and

FIG. 13 shows the filtering device according to a perspective view and in a section composed according to a vertical plane, and a horizontal plane passing through the main axis of the cylinder and a plane orthogonal to the previous planes passing through the main axis of the inlet opening and highlighting the inlet duct of the molten material from the outside of the body to the inside of the chamber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to the drawings, the object of the invention consists of a filtering device, comprising a body 1 with a hollow on the inside that creates a chamber 2. The inside of said chamber 2 houses a hollow perforated cylinder 24 in a rotating manner, and resting against a part of the outer surface 25 of said hollow cylinder 24 is a filtration mesh 26, which in fact is the real filter of the polluting material of the molten plastic.

Said mesh 26 remains attached to a part of the outer surface 25 even with the rotation of the hollow cylinder 24 and in a manner corresponding to the rotation of the hollow cylinder 24, as it rotates with the progression of the rotation, a new section of mesh 26 is engaged and a similar section of mesh is released.

The new section of inlet mesh 6 that engages the outer surface 25 of the hollow cylinder 24 enters the chamber 2 from the outside of the body 1 through an inlet path 6 of the connection opening 5 of the body 1, while the section of outlet-mesh 7 released is led outside the chamber 2 through an outlet path 11 of the connection opening 5.

Said outlet-mesh 7 that comes out of the chamber 2 is clogged with the polluting material of the molten plastic that has adhered to its surface, thereby bringing said polluting material outside the chamber 2.

In fact, the molten plastic material to be filtered enters from the outside of the body 1 into the chamber 2 through a suitable inlet duct 3 that through the body 1 enters the chamber 2 with its own inlet opening, and in particular in that part of the chamber that pertains to the outside of the hollow cylinder 24. After the filtration of the molten plastic material, which passes through the mesh 26 and the holes in the hollow cylinder 24, reaching the inside of the hollow cylinder 24, the material is brought outside the body 1 by means of a suitable outlet duct, through an outlet opening 4.

The force that pushes the molten material to enter chamber 2, to cross the mesh 26 and the holes in the hollow cylinder 24 and to exit the chamber 2 through the outlet duct 4, is exerted by the inlet pressure applied by a special pump or extruder of the molten material.

In a pre-programmed manner or based on expected conditions, such as for example the overpressure of the material, or in a timed manner, all or part of the mesh 26 resting 7 against the outer peripheral surface 25 of the hollow cylinder 24 is renewed with a new mesh 26.

In order to be able to easily renew this mesh 26, the hollow cylinder 24 is rotated and on the outside of the body 1 the mesh 26 at the outlet 8 is driven by a winder/feeder 23.

In order to avoid the pressure in the chamber 2 making it difficult to replace the mesh 26 resting against the outer perimeter surface 25 of the hollow cylinder 24, the pressure is suitably reduced during this operation.

Furthermore, again in order to make it easy to replace the section of mesh resting against the perimeter surface of the cylinder that is blocked, the mobile cone 9 is raised, towards the interior of the chamber 2, widening at least the outlet path 8 and possibly also the inlet path 10, preventing the outlet path 11 and possibly also the inlet path 10, from creating excessive friction in the movement of the outlet mesh 8.

Furthermore, reducing the pressure, during the replacement of the mesh 26, in conjunction with the movement of the cone 9, with the widening of the seats of the outlet 11 and/or inlet 10 paths prevents a considerable quantity of molten plastic material from escaping through the said paths.

Further, the pressure reduction, during the renewal of the mesh 26, in conjunction with the movement of the cone 9, considerably reduces the power required of the actuator 15, associated with the cone 9 in the part facing the outside of the body, that is to the cusp of the cone 16.

In order to reduce the pressure inside the chamber 2 inside the body 1, of the molten material, it is envisaged that this can be possibly implemented by using the pump or extruder outside the body 1.

In the event that it is not possible or appropriate to use the external pump to reduce the pressure of the molten plastic material, the device has at least one of the following characteristics:

-   -   a valved opening 21, which can be controlled, which acts as a         bypass between the inside of the chamber 2 and the outside of         the body 1;     -   a variable volume storage tank 19 with a movable piston 20.

The valved opening 21 is simple to make and effective, providing communication between the inside of the chamber 2 under pressure with the outside of the body 1 at ambient pressure, and a controllable valve 22 is interposed in the communication duct of this opening. When it is necessary to reduce the pressure entirely to the chamber 2 of the molten plastic product, the valve 22 is opened, rapidly decreasing the pressure inside the chamber 2 with the release of a limited quantity of molten material to the outside through the said communication duct of said opening.

In the different way of decreasing the pressure inside the chamber 2, an accumulation tank 19 is provided, connected via a bypass to the internal chamber 2, possibly with a valve, which is made to open and consequently the accumulation tank 19 is filled with the molten material, decreasing the pressure in the internal chamber 2.

Subsequently, once there is no longer a need for a reduced pressure, a movable piston 20 pushes the molten material back into the chamber inside the body which had previously been stored inside the accumulation tank 19.

In the eventuality the valved opening 21 is adopted, and also when the accumulation tank 19 is used, the relative ducts open and preferably connect that part of the chamber where the pressure reduction on the base wall 14 of the mobile cone 9 is more effective, which, for example, could be the one fed and containing the unfiltered molten material, carried directly by the inlet duct 3 of the molten material, i.e. that part of the chamber 2 which relates to the external part of the hollow perforated cylinder 24, with this connection, therefore, the molten material, coming from the extruder or from the pump, is more easily reduced in the overpressure closer to the source thereof.

In any case, facilitated or not by the presence of the pressure reduction devices described above, the displacement of the mobile cone 9 can increase the section of the passage at least of the outlet path 11, and possibly of the inlet path 10, respectively moving the second side wall of the cone 13, and possibly the first side wall of the cone 12 from the side walls that create the connection opening 5 of the body 1.

Effectively, taking into account the friction caused by the sliding of the filtering mesh 26 during its replacement, in the sections in which the inlet mesh 6 and the outlet mesh 8 affect the respective inlet path 10 and the respective path of outlet 11 the walls are protected with plates 17 made with material that is suitably resistant to abrasion by the friction of the filtering mesh 26 moved in the replacement process. 

What is claimed is: 1) a device for filtering molten plastic material, comprising: a body; a cavity inside the body that creates a chamber; a hollow perforated cylinder that rotates around a main axis thereof inside said chamber; an inlet opening on the body for putting the plastic material to be filtered into the chamber; an outlet opening wherein the filtered plastic material comes out from the body, a connection opening that connects the outside of the body with said chamber on the inside of the body; a filtration mesh belt that enters the chamber through the said connection opening and exits through said connection opening after having carried out filtration; a section of inlet-mesh that enters the chamber from outside of the body through an inlet path into the connection opening; a section of adjoining-mesh that remains attached to the outer surface of said hollow perforated cylinder; and a section of outlet-mesh that exits the body from the chamber through an outlet path in the connection opening; wherein said inlet-mesh, said adjoining-mesh, and said outlet-mesh are all a continuous mesh; a mobile cone that creates, together with the body, said inlet path and the said outlet path, wherein said cone can move between a first closing position and a second opening position on the connection opening that connects the outside of the body with said chamber and that, in the first closed position, closes the inlet path with a section of inlet-mesh interposed and closes the outlet path with a section of outlet-mesh interposed, and in the second opening position opens the inlet path and opens the outlet path, wherein said filtering mesh strip can slide in said openings; wherein said inlet path is a first channel between the outside of the body and the inside of the chamber, with a width corresponding to the width of the mesh strip and enclosed between the body itself and a first side wall of the cone; wherein said outlet path is a second channel between the outside of the body and the inside of the chamber, with a width corresponding to the width of the mesh strip and enclosed between the body itself and a second side wall of the cone; and wherein said mobile cone has a base wall between said first and said second side walls, facing the inside of the chamber, and facing the perforated hollow cylinder. 2) The device of claim 1 wherein said base wall of said cone has a profile corresponding to the arc of a circle underlying the perforated hollow cylinder. 3) The device of claim 1 wherein said cone is moved by an actuator connected externally to a cusp of said cone, outside the body. 4) The device of claim 1 wherein said cone and/or said body at the inlet and/or outlet paths of the filtering mesh strip have plates made of a hardened/bonded material, limiting the wear of the corresponding walls during the relative movement of said mesh. 5) The device of claim 1 wherein said body has an opening between the inside of the chamber and a storage tank for storing the molten material when changing and replacing a mesh strip that has become clogged by contamination from the molten material, decreasing the pressure inside the chamber. 6) The device of claim 1 wherein said storage tank is a variable volume tank and has a movable piston that can restrict the capacity of the storage tank, and wherein movement thereof increases the capacity of and facilitates the storage of the molten material coming from the cavity of the chamber, and wherein movement thereof to decrease the capacity facilitates the return of the molten material into the cavity of the chamber. 7) The device of claim 1 wherein said body has a valved opening between the inside of the chamber and the outside of the body so that the chamber can open by operating a valve inserted in said valved opening, releasing the molten material coming from the cavity of the chamber and decreasing the pressure inside the chamber. 8) The device of claim 1 wherein said device has a winder/feeder on the outside of the body for storing, advancing or pulling the clogged mesh strip out of the body. 